Why Crushed Rock is used at the earth surface in the substation?

• We always see crushed rock spread on the surface of soil in the substation. 
• The resistivity of gravel is approximately 2000 ohm – meter whereas the soil resistivity is only 100 ohm – meter. 
• We say that the resistivity of gravel is 20 times than that of soil. 
• The gravel acts as an insulator and back the electric field by the Ground potential rise ( GPR ).

Advantages of Crushed Rock over Soil

• It provides high resistivity at the surface
• Growth of weeds not possible
• People don’t run in the switchyard therefore risk of step potential is reduced
• Reduce moisture of the soil
• Minimize the hazards caused by the movement of reptiles

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